Electron discharge device for ultra high frequencies



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INVENTOR Dec. 14, 1948.` D. G. BuRNslDE i 2,456,579

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ELEoTRoN DISCHARGE DEVICE FOR ULTRA :UGH FREQUENCIES Filed Oct. 30, 1942 y 4 Sheets-Sheet 4 ATTORNEY Patented Dec. 14, 1948 @Limiti ili ELECTRON DISCHARGE DEVICE FOR ULTRA HIGH FREQUENCIES Don G. Burnside, Princeton, N. J., assigner to Radio Corporation of America, a corporation of Delaware Application October 30, 1942, Serial No. 463,972

27 Claims.

My invention relates to electron discharge devices and associated circuits particularly useful at ultra high frequencies.

For certain applications it is necessary to have electron discharge devices which will generate 5 large amounts of microwave power. Tube structures for devices of this type which will satisfy the requirements of high power output at very high frequencies vary from orthodox structures in several particulars.

More important features for such devices are as follows:

The cathode must be capable of providing extremely large emission currents.

Close spacing between electrodes must exist to permit advantageous use of high emission currents.

The tube structures must be such that there ex ists a minimum capacitance between the electrodes, considering other characteristics.

Connections of high conductance and low inductance must be provided between tube electrodes and external circuit.

The insulation used for supports between the electrodes must withstand high voltages and 2" have low losses at high frequencies.

y, All structural designs must be suchl as to peri init large power heat dissipation by thermal conduction and radiation. It is, therefore, an object of my invention toi i Vprovide an electron discharge deviceand associ-` ated circuit particularly useful at ultra high frequencies and capable of generating high power Y Another object of my invention is to provide I, if an electron discharge device in which the cath-"fil ,ode is capable of providing very large emissioni@ currents. A further object of my invention is to provide i such a device having close spacings between elec- ,l

trodes which will enable advantageous use to bei' 40 made of the 'emission currents.

Another object of my invention is tof provide an i electron discharge device of the type described,

l having minimum capacitance between electrodesg A still further object of my inventiony is to pro- 45 vide an electron discharge device andiassociated circuit of the type described in which the connections between the electrodes of the electron discharge device and external circuits are of high conductance and low inductance.

A further object of my inventionis to provide such a device in which the insulation losses are low at high frequencies and thestructural design is such as to provide high power heat dissipation by thermal conduction and radiation.

(CI. Z50-27.5)

A further object of my invention is to provide such a device and circuit which is of reasonable size and economical to operate.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims9 but the invention itself will best be understood by reference to the following description taken in connection with the accompanying drawing in which Figure 1 is a longitudinal section of an electron-discharge device and associated circuit made according to my invention, Figure 2 is an exploded perspecltive of the electrode structure used in the device shown in Figure 1, Figure 3 is a schematic diagram of the tube and circuit and voltage sources of the device shown in Figure 1, Figure 4 is a longitudinal section of a modification of the electron discharge device shown in Figure 1, Figure 5 is an enlarged transverse section taken along the line 5-5 of Figure 4 showing details of the electrode structure, Figure 6 is a detail, partially in section, of the cathode structure employed in the device shown in Figure 4, Figure 7 is a longitudinal section of a still further modification of an electron discharge device and associated circuit made according to my invention, and Figure 8 is an enlarged view partially in section of the cathode employed in the device shown in Figure 7.

In accordance with my invention the electron discharge device is provided with an evacuated envelope I0, enclosing a plurality of cathodes II provided with heaters I2 and surrounded by U- shaped grid structures I3. The anode I4 of a solid mass of conducting material and of truncated-cone shape is provided on its inner surface with a pair of transversely extending channels I4 into which the cathodes and grids are received. The anode is provided with the collar I5 which is sealed to the end of the envelope I0 and a transverse flange I6 from which radiating iins I'I extend. The shape of the anode promotes rapid heat conduction from the electron receiving surfaces to the radiating fins I'I over which cooling air may be blown.

The grid structures shown in greater detail in Figure 2 and which will be described below is supported on a conducting disc 20, in turn supported fromthe grid ring I8 by means of the angular members 2|. The grid ring I8 is sealed through the wall of the glass envelope I0. The cathode structures are supported by means of a cathode disc 22 in turn supported from the cathode ring I9 sealed through the wall of the envelope, the supporting fingers 23 being welded between the ring I9 and the disc 22. In practice the cathode and grid are assembled as a unit and maintained in xed insulated relationship by means of the glass bead spacing structure 24', the cathode and grid being secured to the cathode and grid rings I9 and I8 as a unit during assembly. The cathode heater leads 26 and 21 are cross connected to the cathode heater lead wires 24-25 to put the heater wires in parallel.

The details of the electrode structure are shown in an exploded view in Figure 2. The U-shaped grids I3 are secured to the disc 20 by means of the angle members I3 welded to disc 20, and the grid wires maintained in proper spaced relation by means of the transverse rod I3" at the top of the grid. Thevgrid wires extend through apertures 26' and are welded to the members I3. The cathodes II may be formed of flat ribbon material folded to U-shape and supported from the cathode disc 22 by means of the legs II' and by the U-shaped member II engaging the top of the cathode, the heaters I2 being supported within the fold of the cathodes Il. The outside surfaces of the cathodes II are coated with electron emitting material so that the opposite sides of the cathode each provide a stream of electrons during operation. Cathode heater leads 26 and 21 extend through apertures 22' in disc 22.

As shown in Figures 1 and 2 a by-passing condenser designated generally 28 in Figure 1 for by-passing R.F. currents in the cathode heater leads, includes an insulating disc 29 preferably of mica and segmentally shaped conducting plates 30 and 3|, which plates are provided with legs 32, 33, and 32', 33', to which the cathode heater wires are connected. This by-passing condenser is completed by means of insulating discs 34 and 35, and clamping plates 36 and 31, the entire assembly including disc 22 being secured together as a unit.

As shown in Figure 1 the input circuit cornprises a resonator of the coaxial line type and includes outer cylinder 4B, inner cylinder 4I, one being closed by member 42 and the other by member 43. The cathode ring I9 is capacity coupled to the inner cylinder 4I by means of the collar 45 insulatingly supported from the inner cylinder 4I by the insulating collar 44, the collar 45 being provided with spring ngers 45' engaging the rim of the cathode ring I9. The closure wall 43 is provided with spring ngers 46 which contact the outer rim of the grid ring IB. Thus the R. F. voltage within the resonator appearing across the space between the members 45 and 46 is impressed between the cathode and grid When the input resonator is excited.

An external voltage may be applied to the cathode by means of the conductor 45" electrically secured to the conducting collar 45.

The output circuit includes a resonator formed by the members 43 and 41 and the collar 48. The anode is capacity coupled to the wall 41 by means of the collar 49 engaged by spring fingers 50 fastened to the collar I, which is capacity coupled through the-insulating collar 53 secured to the collar 52 on the wall 68 of the resonator. Since the anode is insulated from the tank circuit for D. C., a different xed potential may be applied to the anode than to the tank.

Energy may be coupled back from the output tank circuit to the input circuit by means of a -t'rarnsmission line, including coupling loop 54 rotatable about an axis lying in the plane of the drawing, by means of rotating kn'ob 55, to increase or decrease the amount of couplng- The as over the radiating fins I1.

transmission line 56 is hollow and telescopically connected with the loop 51 supported by means of the sliding clamp 51' slidable in the slot 58 of the inner tubular member 4I of the input resonator. The output may be taken by means of the loop 68 which terminates in the coaxial transmission line 6I.

The formation and arrangement of the cathode is such that a large emitting area is provided to produce large emission currents without unduly increasing the heating power required. The shape of the grids, cathodes and anode is such that close spacing of all electrodes is permitted to take advantage of the high emission current. Because of the arrangement of the grids and their supports, and the fact that the grid is operated at ground potential, the input and output circuits are completely shielded from each other, reducing the capacity coupling between the cathode and the anode and permitting critical control of the feedback by means of the coupling loop and feedback arrangements. The ring supports offer high conductance and low inductance between the tube electrodes and the tank circuit, and the anode design is such as to readily dissipate large amounts of heat which may be generated in the anodes, since the mass of the anode increases toward the exterior of the envelope, permitting ready ow of heat away from the electron receiving surfaces of the anode channels and dissipation by means of the radiating ns I1. If desired the resonant cavities may be provided with apertures through which a cooling medium can be directed over the ring seals as well The arrangement of the electrode supports within the envelope and the design of the resonator circuits are such as to readily provide for engagement and disengagement of the electron discharge device and circuits. Thus by means of my invention all of the desirable characteristics are provided.

A schematic diagram of an electronkdischarge device and circuit according to my invention with associated power supplies is shown in Figure 3. The cathode heater is supplied by means of transformer 62. Since the grid and tank circuit are grounded at 63, and the cathode and anode, with no exciting voltage applied, are at substantially the same potential, no current normally flows. When it is desired to permit the flow of current to excite the output resonator, a Voltage differential is applied between the cathode I I and anode I4 by means of the pulsing transformer 64. A safety overload device consisting of a condenser and a spark gap is inserted between the anode and the transformer 64. Resistor 66 is for the purpose of supplying a biasing voltage between grid and cathode.

A modification of the structure shown in Figure 1 is shown in Figures 4 to 6 inclusive. In Figures 4 to 6, inclusive, the same numerals designate the same parts as in Figure 1. The construction of the electron discharge device shown in Figure 4 differs from that shown in Figure 1 in the electrode arrangement. The anode 10 of truncated-cone shape is provided with an annular channel of elongated U-shape transverse section and into which the indirectly heated annular cathode 12 and grid 13 extend. The grid is supported from the grid disc 14 again secured to and supported by grid ring I8, and the cathode is supported by means of the cathode disc 15 supported from the cathode ring I9 by means of the supporting members 16. One of the cathode heater leads of each cathode heater -is connected to the lcathode -disc or Vplate 15 and the other lead to ring 11 insulatingly supported from disc 15. The disc 15 is electrically connected to lead 24 and ring 11 lto lead 25. The cathode and grid structures are again assembled as a unit externally of the tube and then mounted on rings I8 and |9 within the tube.

In order to properly space the grid from the anode a stop member 11' of insulating material may be supported on the cathode disc and is received within the anode. The relation of the cathode, grid and anode is shown in the large transverse cross sectional view of Figure 5 taken along section 5-5 of Figure 4.

As shown in Figures 5 and 6 the cathode is made of concentric collar-like members 12 and 12 spaced by means of spacer rods 18, the cathode being heated by a plurality of cathode heater units 19 positioned within the cathode between the members 12 and 12'. The upper end of the cathode cylinders may be closed by means of ring-like member 12".

This apparatus functions in substantially the same manner as shown in Figure l and has all of the inherent advantages of the structure shown in Figure 1 plus a greater possible cathode area within an equivalent anode (or envelope) bulk.

A still further modication of my invention is shown in Figure '1. In this modification the envelope 80 is closed at one end by means of the anode comprising two parts 8| and 82 and secured together by means of the screw 83. The device is made in the manner shown to permit assembly of the grid and cathode Within the annular channel 84 extending around the circumference of the anode. However, in heat dissipation properties the two parts of the anode may be considered a solid mass of conducting material, as in Figs. 1 and 4. The cathode 85 is surrounded bythe grid 86 which is supported from the gri'dfpring 8 by means of supporting eleI-ents 89. The cathode in turn is supported from the cathode ring 88 by means of the structure 90 including the conducting ring 9| and supporting members 93. A second conducting ring 92 is supported from the ring 9 I'. One of the cathode heater leads of each cathode heater is connected to the conductors 93 and the other of the cathode heater leads 94 is connected to th-e cath-ode heater ring 92, the connection to the source of heating voltage being by means of the leads and conductors 95 and 96.

As shown by the enlarged View partially in section in Figure 8, a cathode is made of a pair of flat ring like members 85-85' separated by means of rods 91 and supporting between them the heaters 85". The inner edges of the rings are closed by means of the conducting member 98.

The input circuit comprises the resonator including the cylinder members 99-I00 closed by means of member The output resonator includes members |02, |03 and |04. Energy is taken from the output resonator by means of the loop and energy is fed back into the input circuit by means of adjustable loop |06 and loop |01 adjusted by means of operating handle |08. Contact between the electrode elements and the input and output resonators is made by means of conducting contact ngers |09, ||0 and the anode being insulated from the output resonator by means of insulating collar ||2 and the cathode from the input tank circuit by meansY of the insulating collar I3.

The apparatus shown in Figure '1 also functions in a manner similar to the device shown in Figure 1.

While I have indicated the preferred embodiments of my invention of which I am now aware and have also indicated only one specific application for which my invention may be employed, it

5 will be apparent that my invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope of my invention as set forth in the appended claims.

What I claim as new is:

l. An electron discharge device having an elongated envelope closed at one end by an anode, said anode being sealed to said envelope and extending inwardly of said envelope, the inner end of said anode being of smaller transverse section than the part sealed to said envelope, said anode having a channel extending transversely of the inner end and a cathode and grid supported within said channel, said cathode being of fiat construction and having oppositely disposed emitting surfaces registering with the opposite faces of said channel, the grid being positioned between said cathode and said anode.

2. An electron discharge device having an elongated envelope closed at one end by an anode, said anode being sealed to said envelope and extending inwardly of said envelope, the inner end of said anode being of smaller transverse section than the part sealed to said envelope, said anode having a channel extending transversely of the inner end, and a cathode and grid supported within said channel, said cathode being of flat construction and having oppositely disposed emitting surfaces registering with the opposite faces of said channel, the grid being positioned between said cathode and said anode, said anode having a flange extending transversely of the envelope and a rst resonator coupled between the cathode and grid and a second resonator coupled between said grid and anode, said grid being directly connected to said resonators and said cathode and anode flange being capacitively coupled to said resonators.

3. An electron discharge device having an elongated envelope closed at one end by an anode, said anode being sealed to said envelope and extending inwardly of said envelope, the inner end of said anode being of smaller transverse section than the part sealed to said envelope, said anode having a channel extending transversely of the inner end and a cathode and grid supported within said channel, said cathode being of flat construction and having oppositely disposed emitting surfaces registering with the opposite faces of said channel, the grid being positioned between said cathode and said anode, said anode having a flange extending transversely of the envelope, radially extending conducting supports extending through the wall of the envelope and supporting said cathode and said grid, and a first resonator coupled between the cathode and gridV Aand a second resonator coupled between saidI grid and anode, the grid support being directly (connected to said resonators and the cathodev support and said anode ange being capacitively coupled to @./sai'd resonators.

ji. An electron discharge device having an -elongated envelope closed at one end by an anode, said anode being of a truncated longitudinal section and sealed to said envelope and extending inwardly of said envelope, the inner end of said anode being of smaller transverse section than the part sealed to said envelope, said anode having a deep channel extending transversely of its inner end and a cathode and grid supported within said channel, said cathode being of iiat construction and having oppositely disposed emitting surfaces registering with the opposite faces of said channel, said anode having a flange extending transversely of the envelope and an input resonator coupled between the cathode and grid, and an output resonator coupled between said grid and anode, said grid being directly connected to said resonators and said cathode and anode being capacitively coupled to said resonators, and a transmission line for transferring energy between said resonators and including a rotatably mounted coupling loop at one end Within said output resonator and an adjustable coupling loop at the other end of said transmission line within said input resonator.

5. An electron discharge device having an anode comprising a solid conducting mass of truncated shape, said anode having a transverse channel extending across the smaller end of said anode, a flat cathode supported Within said channel and having oppositely disposed emitting surfaces registering with the opposite faces of said channel and a grid member of U-shape positioned between the cathode and the anode within said channel, a. transverse conducting member supporting said grid and a second transverse conducting member supporting said cathode, said conducting members being secured in xed spaced relation, ring-like supports andgnducting leads secured to said cathode and said grid conducting members, and an envelope enclosing said cathode, grid and anode.

6. An electron discharge device having an anode comprising a solid conducting mass of truncated shape, said anode having a transverse channel extending across the smaller end of said anode, a flat cathode supported within said channel and having oppositely disposed emitting surfaces registering with the opposite faces of said channel and a grid member of U-shape positioned between the cathode and the anode within said channel, a transverse conducting member supporting said grid and a second transverse conducting member supporting said cathode, said conducting members being secured in Xed spaced relation, ring-like supports and conducting leads secured to said cathode and said grid conducting members and an envelope enclosing said cathode, grid and anode, the larger end of said anode being provided with a transverse ange sealedgtdsaid envelope.

7. An electron discharge device having an anode comprising a solid conducting mass of truncated shape, said anode having a transverse channel extending across the smaller end of said anode, a at cathode supported within said channel and having oppositely disposed emitting surfaces registering with the opposite faces of said channel and a grid `member of U-shape positioned between the cathode and the anode Within said channel, a transverse conducting member supporting said grid and a second transverse conducting member supporting said cathode, said conducting members being secured in fixed spaced relation, an envelope enclosing said cathode, grid and anode, ring-like supports and conducting leads secured to said cathode and said grid conducting members, said ring-like supports extending through and sealed to said envelope, the larger end of said anode being provided with a transverse flange sealed to said envelope, said cathode and grid ring supports and conducting leads and said anode flange being adapted to be engaged by spring nger contacts of resonators connected between the cathode and grid, and the grid and the anode.

8. An electron discharge device having a cathode assembly including a conducting plate, a cathode proper supported from one side of said plate and a heater within said cathode provided with a pair of heater leads, said plate having an aperture through which said heater leads extend, an insulating member mounted on the other side of said plate from said cathode, and a pair of at conducting elements mounted on said insulating member and insulated from said plate, one of said heater leads being connected to one of said at conducting elements and the other of said heater leads being connected to the other of said flat conducting elements.

9. A cathode assembly for an electron discharge device including a conducting plate having an aperture centrally thereof, a flat cathode supported from one side of said conducting plate in a plane transverse to said plate, a heater for said cathode and having a pair of heater leads, an insulating member mounted on the other side of said conducting plate from said cathode, and having an aperture registering with the aperture in said plate, a pair of conducting members mounted on said insulating member and oppositely disposed from said plate, said pair of conducting members having legs, one of said heater leads being connected to a leg of one of said pair of conducting members and the other of said heater leads being connected to a leg of the other of said pair of conducting members, and means for securing said plate, insulating member and said pair of conducting members together as a unit.

10. A cathode electrode assembly for an electron discharge device including a conducting plate-like member having a central aperture, a plurality of ilat cathodes mounted and supported from one side of said conducting plate and perpendicularly to said plate, cathode heaters positioned within and supported by said cathodes, each of said heaters being provided with a pair of leads, an insulating member secured to the opposite side of said conducting plate from said cathodes and a pair of conducting members mounted on said insulating member and provided with legs, one lead of each of said heaters being connected to a leg of one of said pair of conducting members and the other heater lead of each of said heaters being connected to a leg of the other of said pair of conducting members, and means securing said conducting plate, insulating member and pair of conducting members together as a unit.

11. An electron discharge device having an anode increasing in transverse section from one end of said anode to the other, said anode having an annular channel formed in the smaller end thereof, said channel being of elongated transverse section, a collar-shaped cathode positioned Within said channel and a grid positioned between said cathode and said anode.

12. An electron discharge device having an anode comprising a solid mass, said anode having an annular channel formed in surface thereof, said channel being of elongated transverse section, a collar-shaped cathode positioned within said channel, a conducting member to which said cathode is secured and upon which said cathode is supported and a conducting ring insulatingly supported on said conducting member and a heater for said cathode having a, pair of heater leads, one of which is connected to said conducting member and the other of which is connected to said conducting ring.

13. An electron discharge device having an anode of solid mass increasing. in transverse section from one end of said anode to the other, said anode having a deep annular channel formed in one end thereof, a collar-shaped cathode positioned within said channel and a grid positioned between said cathode and said anode, a flat conducting member to which said cathode is secured and upon which said cathode is supported, and a conducting ring lying parallel to said iiat conducting member and supporting said grid, said cathodeand grid being mounted in xed spaced relation as a unit, and means supported on said flat cathode supporting conducting member and contacting said anode for determining the spacing between the cathode, grid and anode.

14. A cathode for an electron discharge device comprising a pair of concentric collar-likemembers, means spacing and securing said collar-like members together and a plurality of heater members mounted between said collar-like elements of said cathode, only those surfaces of said collarlike members opposite the surfaces exposed to said heater elements being coated with electron emitting material.

15. A cathode for an electron discharge device comprising a pair of concentric collar-like members, means spacing and securing said collar-like members together and a plurality of heater `elements mounted between said collar-like members'of said cathode, said collar-like members being provided with conducting supporting legs and a conducting disc member to which said legs are secured.

16.. A cathode for an electron discharge device comprising a pair of concentric collar-like members, means spacing and securing said collar-like members together and a plurality of heater elements mounted between said collar-like members of said cathode, said collar-like members being provided with conducting supporting legs and a conducting disc member to which said legs are secured, and a conducting ring insulatingly supported on the opposite side of said disc-like member from said cathode, each of said heater elements being provided With a pair of leads, one of said leads being connected to said conducting disc member and the other of said leads being connected to said ring.

1'7. An electron discharge device having a twopart anode, each of said parts being of plate-like shape with a centrally positioned raised portion, said raised portions being in contact providing oppositely disposed faces forming an annular channel of elongated transverse section, a flat ring-like cathode positioned within said channel and a grid positioned between the cathode andv the. surfaces of said channel, and means supporting said cathode, grid and anode in spaced rela- -tion.

. :10 which said grid is secured and connected 'and' a second conducting ring to which said cathode is secured and connected.

19. An electron discharge device having a twopart anode, each of said parts being of plate-like shape with a centrally positioned raised portion, said raised portions being in contact providing oppositely disposed faces forming an annular channel of elongated transverse section a at ring-like cathode positioned within said channel and a grid positioned between the cathode and the surfaces of said channel, and means supporting said cathode, grid and anode in spaced relation, said means including a conducting ring to which said grid isv secured and connected and a second conducting ring to which said cathode is secured and connected, and an envelope for said cathode, grid and anode,4 said rings extending through and sealed to the wall of said envelope, said anode being sealed to and closing one end of said envelope.

20. An electron discharge Adevice having a twopartl anode, each of said parts being `a, plate-like shape with a centrally positioned raised portion, said raised portions being in contact providing op- -positely disposed faces forming an annular channel of elongated transverse section, -a iiat ring-like cathode positioned Within said channel and a grid positioned between the cathode and the surfaces of said channel, and means supportingsaid cathode, grid and anode in spacedrelation, said means` including a conducting ring to which said grid is secured and connected and a second conducting ring to which said cathode is secured and connected, and a pair of ring-like members supported on said cathode ring, one of said ring-like members being electrically connected to the cathode ring and the other of said ring-like members being insulatingly supported from said rst ring-like member, a cathode heater for said cathode and having a pair of leads, one of said leads being connected to one of said ring-like members and the other of said leads being connected to the other of said ring-like members.

21. An electron discharge device having an aYlOde Comprising 'a mass of conducting material and having a portion of circular transverse cross section, said elongated portion having an annular channel lying in a plane transverse to the longitudinal axis of said anode and a flat ring-like cathode positioned within said channel and means maintaining said -cathode and anode in fixed spaced rel-ation.

22. An electron discharge device having an anode comprising a solid mass of conducting material, said anode having at one end a transverse flange and provided adjacent its other end with an annular channel lying in a plane transverse to the longitudinal raxis of said anode, la flat ring-like cathode positioned within said channel and a grid between said cathode and the walls of said channel, and an envelope for said grid, cathode and anode, the ange of said anode being sealed to said envelope.

23. A cathode for an electron discharge device and -comprising a pair of spaced iiat ring-like members, means maintaining said ring-like members in xed spaced relationship and a plurality of heaters positioned between said rings for heating said cathode, only the surfaces of said plates opposite the surfaces exposed to said heaters being coated with electron emitting material.

24. A cathode for an electron discharge device comprising a pair of flat ring-like members, conducting rods r-adially positioned between said iiat ring-like inei'bers and secured to said ring-like members to maintain them in fixed spaced rela tionship, a ring element adjacent the inner edges of the iiat ring-like members closing lthe space between thev ring-like members and a plurality of heater elements positioned between the flat ringlike members and between the radially positioned rods for heating said cathode.

25. An electron discharge device having an elongated cylindrical envelope closed at one end by an anode, said anode comprising a solid mass of conducting material of truncated-cone shape having its larger diameter end sealed to said envelope and its smaller diameter end extending within said envelope, ra plurality of heat radiating ns secured to and extending outwardly from said larger diameter end of said anode, said anode having a deep channel in its inner end, :a cathode supported within said channel and having oppositely-disposed emitting surfaces of large area registering with the opposite faces of the channel, and a grid positioned between the cathode and the anode.

26. An electron discharge device according to claim 25, wherein said grid has a U-shaped transverse section, and said heat radiating fins extend parallel to` the longitudinal axis of said anode.

27. An electron discharge device having an elongated envelope closed at one end by an anode, said anode `comprising a solid mass of conducting material and being sealed at one end 4to said envelope with the opposite end extending inwardly of said envelope, the inner end of said anode being of substantially smaller transverse section than Ithe end sealed to said envelope, said anode having a channel in its inner end, a cathode supported in `said channel and having oppositely-disposed emitting surfaces registering with the channel walls, and a grid positioned between said cathode and said anode. .r

DON G. BURN-SIDE.

REFERENCES CITED The following references are of record in the le of this patent:

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